The subject matter disclosed herein relates to composite laminate tooling and, more particularly, to tail rotor blade flexbeam tooling.
A rotor blade flexbeam is a primary structural element of a helicopter tail rotor blade assembly inasmuch as its primary function is to transfer combined flapwise, edgewise and centrifugal loads to and/or from a central torque drive hub member. These features are sometimes formed with fiber reinforced resin matrix composite materials due to their advantageous strength-to-weight ratios, however, widespread use thereof has been impeded despite the inherent weight and strength advantages by the high cost of materials and associated fabrication methods.
Conventional methods for manufacturing composite flexbeams include prepreg lay-ups of composite material. Although effective, these processes are relatively time and labor intensive. Normally, prepreg lay-up processes are primarily performed by hand and prepregs have little structural rigidity in their uncured state. The prepregs are hand-stacked and interleaved upon a tooling surface with tooling side walls, which provide the reaction forces at the perimeter profile of the flexbeam. The tail rotor flexbeam is then finished using autoclave processing and employment of a composite caul plate to transfer pressures and to control spar dimensional tolerances during the cure process.
The prepreg lay-up process of stacking composite materials into a female tooling mold cavity is prone to thickness variability and poor composite quality. Additional, destructive quality coupon testing is performed on all specimens where the specimens are removed before final machining such that minimum coupon strength is required for quality control to insure that process variability meets engineering specifications. In addition, existing processes for rectangular components cannot easily direct fibers in off-axis axial directions. They also create a part that is oversized and must be trimmed later in a subsequent operation. The resultant of the machining is cut fibers in the axial direction that when subjected to tension fatigue loads can splinter and propagate into the laminate. Moreover, a typical automated fiber placement machine head may be very large for handling and working with flexbeam composite tooling.